The prevalence of childhood obesity has reached epidemic proportions and ranks among the most prevalent chronic conditions of children, while national trends indicate insufficient and declining levels of physical activity among children. When energy intake exceeds energy expenditure an energy gap ensues, leading to weight gain. The design of buildings and neighborhoods, known collectively as the built environment, has the potential to influence physical activity levels. Promoting active use (i.e. walking, riding a bicycle) of the built environment may produce a small daily increase in physical activity which could close the energy gap. The aim of this research is to study a strategy for increasing physical activity in children by increasing use of built environment. This research will use Geographic Information Systems (GIS), global positioning systems (GPS), and accelerometers to determine where, and to what extent, children aged 10-16 years engage in physical activity in their neighborhoods, and test whether applying this information in the office setting can enhance physical activity counseling. This proposal represents a collaborative cross-disciplinary approach to physical activity research that bridges the design (architecture and urban planning) and health professions. The overall aim of this five-year study is to collect information on children's use of the built environment and determine whether this information can be used in the office setting to counsel overweight children on increasing their physical activity. The specific aims of this study are: 1) to use personalized GIS, GPS, and accelerometer data to identify the built environment elements most associated with physical activity in adolescents in order to define the empiric content of physical activity counseling, 2) to explore, using qualitative methods, what factors would maximize adolescents' receptivity and use of the empiric information identified in Specific Aim1 to increase physical activity, and 3) to develop and test the feasibility of a pediatric physical activity intervention that incorporates personal information on use of the built environment, and test the intervention's preliminary efficacy at increasing physical activity and closing the energy gap. This research will introduce new approaches to understanding and increasing activity among children by testing the feasibility of an intervention that offers novel options for promoting activity in the pediatric office setting, including offering physical activity opportunities which are personalized and flexible. As such, this proposed research has the potential to increase children's physical activity levels and is consistent with the NHLBI's goals and We Can! program (Ways to Enhance Children's Activities and Nutrition) aimed at increasing physical activity among children. The study will also collect preliminary data assessing whether an intervention that promotes active use of the built environment increases use of the built environment and physical activity, data that will allow for the determination of an effect size and sample size needed for a larger R01 study assessing whether promoting active use of the built environment results in sufficient energy expenditure to close the energy gap.